Needlestick injuries among medical practitioners is and has been of tremendous concern because of the possibility for transmission of diseases, for example, the AIDS and Hepatitis B and C viruses and numerous other blood-borne pathogens. The vast majority of currently commercially available syringes do not protect the medical practitioner or those individuals involved in the disposal of syringes from needlestick injuries and consequent possibility of contracting these diseases.
A number of patents disclose syringes having needle-protecting features but most, for various reasons, have not appeared to any significant extent in the marketplace. See, for example, U.S. Pat. Nos. 4,592,744; 4,804,370; 4,542,749; 4,631,057; 4,425,120; 4,258,713; 4,266,544; 4,139,009; 4,774,964 and 4,507,117. These patents have addressed the problem in various ways but none have completely solved the problem or have been a commercial success.
The present invention is a result of various refinements made to assignee's efforts to design, develop and market a safety syringe of the type in which the needle is retractable within the syringe barrel and sealed. Prior syringe designs of applicants' assignee are reflected in U.S. Pat. No. 5,688,240, issued Nov. 18, 1997 and antecedent patents of assignee. While assignee's design demonstrates superior capabilities vis-a-vis the designs of the above-listed prior patents, further refinements as set forth herein are believed necessary to provide a fail-safe, easily usable retractable needle syringe. For example, in the prior design illustrated in assignee's U.S. Pat. No. 5,688,240, the disclosure of which is incorporated herein by reference, the connection between the plunger and needle-carrying adapter could be disrupted by forceful withdrawal of the plunger subsequent to that connection and prior to complete unthreading of the adapter relative to the barrel. While this might occur only rarely, if at all, there remained the possibility that the adapter could be left in the barrel end in a loosened condition leaving exposed a contaminated needle and potentially permitting leakage of fluids from the syringe. Additionally, while assignee's prior patent demonstrated a capacity to seal both ends of the syringe barrel for disposal, it relied on a threaded connection between the proximal end of the plunger, after it was broken off from the adapter, for threaded sealing engagement with the distal end of the barrel. While both ends of the barrel were fluid-sealed, this resulted in an elongated structure which, from a disposal standpoint, disadvantageously increased trash volume. Other refinements and improvements to assignee's prior syringe will be evident from the ensuing description.